I am a newbie. I like the Mesa. I was not sure about which bike is better though. I bought a Next Mountain Ridge from WMart, which looked nice with disc brakes and all too, but gears were kind of noisy. So I retuned that after 2 days.

My friend bought Boulder SE which looked good too.

Schwinn is sold everywhere and Giant seems to be a premium bike brand, that's why I am confused.

Sounds like you bought the right bike this round. When buying new at that price range your better off with V-brakes , doubble the price paid & you can get into better components. Just go ride & whoop on your friends!! Almost any bike is going to need adjusting.